Fix code warning.

Change-Id: Ib11fb49f528d3688351ae349d5b4e307c28b3967
diff --git a/mbtk/libmbtk_lib/tcpip/mbtk_tcpip_at.c b/mbtk/libmbtk_lib/tcpip/mbtk_tcpip_at.c
index fadb1a6..967e7fa 100755
--- a/mbtk/libmbtk_lib/tcpip/mbtk_tcpip_at.c
+++ b/mbtk/libmbtk_lib/tcpip/mbtk_tcpip_at.c
@@ -500,7 +500,7 @@
     }
 
     if(tcpip_link[link_id].type == MBTK_TCPIP_TYPE_CLIENT) {
-        if(tcpip_handle, tcpip_link[link_id].tcpip_info.cli_info.read_cb) {
+        if(tcpip_handle && tcpip_link[link_id].tcpip_info.cli_info.read_cb) {
             LOGE("Set read_cb function,can not manual read.");
             return -1;
         }